The development of a rat model (the borderline hypertensive rat, or BHR) which shows chronic blood pressure elevations following environmental perturbations, as well as the use of human subjects with a genetic history of hypertension (HT), means that, for the first time, studies can be designed which attempt to delineate both the mechanisms of environmentally-induced HT and the relationship between acute and chronic blood pressure elevations. Furthermore, since stress-induced HT can be significantly attenuated by exercise training in the BHR, it is now possible to begin to delineate the mechanisms for the protective effects of exercise. That exercise should have a protective effect is somewhat enigmatic, due to the similarity of cardiovascular (CV) responses to both exercise and psychological stressors. In the present proposal systematic comparisons of the CV, renal and endocrine responses produced by both stressors are proposed. Specifically, the first study will compare the CV, plasma catecholamine and renin responses to aerobic exercise, adjusted for fitness level, in young men with and without a positive parental history of hypertension and who display varying degrees of CV reactivity. The primary purpose of this study is to obtain an unambiguous marker of sympathetic nervous system differences in individuals with and without a predisposition to develop hypertension. The remaining studies will use the BHR. Of these, the first will directly test the hypothesis, formulated from human studies, that CV reactivity is related to a susceptibility to develop hypertension. In this study the degree of CV reactivity shown in young BHRs (8-10 weeks) will be correlated with the extent of hypertension resulting from 12 weeks of chronic stress. The second study will take advantage of the fact that exercise elicits many of the same acute responses as psychological stress in the absence of any deleterious consequences on blood pressure. Thus, exercise serves as a valuable probe of physiological function and an excellent means of distinguishing responses associated with pathology from those common to all physiological arousal (i.e., a stress control condition). This experiment will involve the comparison of the urinary excretion of sodium (NA), potassium (K), norepinephrine and epinephrine in metabolic chambers, in rats exposed to either daily swim training, electric shock, both or neither intervention over a 12 week period. At termination, a third study will examine the changes in catecholamines (CA) and their metabolites in hypothalamic and brainstem nuclei resulting from these protocols. In the fourth and fifth studies hemodynamic (cardiac output, total peripheral resistance) and renal function, respectively, will be delineated in rats exposed to chronic stress, exercise training, both or neither intervention for 12 weeks.